Gas cell-based laser ion sources: Production and study of exotic nuclei Iain Moore JYFL, Finland

 General introduction to RIB production  Practicalities of ion survival in gas  In-gas cell laser resonance ionization  Gas jet laser ionization  Case examples and outlook Outline of talk I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

The nuclear physicists playground J. Erler et al., Nature 486 (2012) 509 ~ 7000 bound nuclei between 2<Z<120 >3000 experimentally observed Nuclear structure Nuclear astrophysics Fundamental physics Applications Our boundaries Our questions I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

< M. Huyse I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct New discoveries with new techniques Reactors: n on U First ISOL experiments Selective detection :  decay Light-ion induced spallation Heavy-ion induced fusion Projectile + target fragmentation; In-flight separation Radioactivity discovered

The ISOL method of RIB production High-energy primary beam Radioactive atoms Low-energy ion beam Mass selection kV High yield but difficult for refractory elements, chemically active elements. Z and T 1/2 dependence First developed in 1951, Niels Bohr Institute I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct ISOL facilities: TRIUMF (Canada), GANIL (France), ALTO (France), ISOLDE (Suisse), ORNL (USA) (SPES, HIE-ISOLDE, ARIEL) Talk: B. Marsh

High-energy primary beam Projectile fragments Isotope selection Medium-energy ion beam The in-flight method of RIB production Very fast separation: μ s half-lives Beams of ALL elements. Often poor beam quality. Precision experiments not directly accessible. First in-flight separator, Oak Ridge (1958) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct GANIL (France), GSI (Germany), NSCL/MSU (USA), RIBF RIKEN (Japan), (FRIB, FAIR)

The ion guide / gas catcher method …an ISOL system for ALL elements, fast extraction Projectile source Thin target mass separator Fast beams Purification in-flight Electrical fields ``The best of both worlds´´ I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Ion survival Ion guide technique Neutralization Laser re-ionization Z selectivity

What do we mean: nuclear reaction? I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct What do we mean by a nuclear reaction? Task 1: create a source of 56 Co and calculate the rate of production Handout 1

 General introduction to RIB production  Practicalities of ion survival in gas  In-gas cell laser resonance ionization  Gas jet laser ionization  Case examples and outlook Outline of talk I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- + β e-e- * primary/secondary beam Stopping Neutralization - 3 body Molecular formation: atoms and ions Diffusion losses Decay losses + Metastable state He or Ar few 100 mbar Photo ionization Complexity of gas cell processes High density gases to stop energetic particles High IP of noble gas atoms prevents charge exchange between ions and buffer gas atoms

I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Molecular ion formation X + + M → XM + dn/dt = -kn[M]  = 1/k[M] ReactionRate constant k (cm 3 s -1 ) Mo + + O 2 Ru + + O 2 Rh + + O 2 Ti + + H 2 0 Ti + + O 2 Y + + O 2 Th + + O 2 U + + O 2 Zr + + O 2 Ag + + O 2 7.5× × × × × × × × × × Laser beams Exit hole Ar/He from gas purifier Filament (yttrium) Towards mass separator SPIG Ar 500mbar

 = 5.1(4) ms  = 96(10) ms I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Effect of impurity levels in the gas Question: What impurity levels do these timescales correspond to? T. Kessler, I.D. Moore et al., NIMB 266 (2008) 681 Laser on

C He (l/s) = 0.45·d(mm) 2 C Ar (l/s) = 0.14·d(mm) 2 t evac = V/C I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Lets add some beam from our cyclotron Ionization processes Recombination processes Space charge effects Effective volume for laser ionization <1% of the ion guide volume Laser ionization must be applied in a region of low ion-electron density I.D. Moore et al., NIMB 268 (2010) 657 Laser beams Target (~ mg/cm 2 ) Cyclotron beam Exit hole Ar/He from gas purifier Filament Towards mass separator SPIG Ar 500mbar How can we suppress this ”plasma”?

Yu. Kudryavtsev et al., NIM B 267 (2009) 2908 Laser beams Longitudinal SPIG Ar/He from gas purifier Ion Collector Ionization chamber Beam from Cyclotron Target Exit hole Ø 0.5 – 1 mm M. Reponen, I.D. Moore et al., NIMB 317 (2013) 422 Separation of stopping and laser ionization volume improves: Laser ionization efficiency at high cyclotron beam current Increasing selectivity (collection of non-neutral ions) Separate the plasma and ionization chambers I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Ni(p,n) 58 Cu (τ ½ =3.2s) Eff. ~ 1%

 General introduction to RIB production  Practicalities of ion survival in gas  In-gas cell laser resonance ionization  Gas jet laser ionization  Case examples and outlook Outline of talk I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

~6 eV (5-9 eV) ground state first excited state higher excited states IP E1E1 energy 0 eV E0E0 non-resonant ionization excitation of auto-ionizing states ionization of Rydberg-states extraction field or collisional ionization  R ~ cm 2   ~ cm 2   ~ cm 2 SELECTIVITY & EFFICIENCY At Just in case you forgot…… I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct B. Marsh; K. Wendt

The nuclear fingerprint on the atomic structure Sizes Spins Q s μ Model Independent (measured) 20 μ eV Isotope shift  Isomer shift  Hyperfine Splitting Model Dependent (inferred) Dynamic / static deformations Single / few particle configurations Y+Y+ I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct STABLE MORE NEUTRON RICH

Workhorse: Collinear fast beam laser spectroscopy 0 Doppler broadened profile Applied Doppler tuning voltage 30-60kV CW tunable laser beam (~1mW, few MHz) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

In-source RIS vs. collinear spectroscopy Selective process Short lifetimes, low yields (<1 ion/s) High detection efficiency Poor resolution ( × < CLS) Cu   I. Stefanescu et al., PRL 98 (2007) (g.s.) IN-SOURCE (RIS) Cu P. Vingerhoets et al., PRC 82 (2010) COLLINEAR High resolution Scanning voltage, not frequency Detect photons Beams of some 10 3 ions/s I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Broadening of atomic transitions (I) Power broadening For RIB production we want optimum efficiency For spectroscopy we trade efficiency for spectroscopic resolution I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Natural linewidth: 135 MHz V. Sonnenschein, I.D. Moore et al., EPJA 48 (2012) 52

Broadening of atomic transitions (II) When an atom is in thermal motion we get Doppler broadening. An atomic vapour has a Maxwell-Boltzmann distribution of velocities: ν0ν0 I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Doppler broadening 232 Th Hot cavity Crossed beams Natural linewidth: 35 MHz Spectral linewidth: 2.4 GHz (hot cavity) ~ 170 MHz (crossed beams) Crossed beams and collinear are basically Doppler-free

Broadening of atomic transitions (III) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Pressure broadening + shift T. Sonoda et al., NIMB 267 (2009) 2918 Ni Cu Ar gas Broadening Shift 11 MHz/mbar 5 MHz/mbar -6 MHz/mbar -2 MHz/mbar

Limitations of the gas cell approach I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct  br =32(4) MHz/mbar Laser spectroscopy on Sn isotopes Large pressure broadening coefficient for λ 1 Extraction of hyperfine structure very difficult  sh = 150(10) MHz/mbar R. Ferrar et al., NIMB 317 (2013) 570

 General introduction to RIB production  Practicalities of ion survival in gas  In-source laser resonance ionization  Gas jet laser ionization  Case examples and outlook Outline of talk I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Gas jet laser ionization – how and why? I.D. Moore et al., AIP Conf. Proc. 831 (2006) P 3/2 2 P 1/2 2 S 1/2 FjFj FiFi an optimal environment for spectroscopy (reduced temperature and pressure) F=J+IF=J+I N N S S I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct a quest for PURE radioactive ion beams → (the Laser Ion Source ``Trap´´) B. Marsh

Yu. Kudryavtsev et al., NIMB 297 (2013) 7 An “ideal” cold environment for resonance ionization spectroscopy I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Temperature vs. Mach number nm 4s 2 S 1/2 → 4p 2 P 1/2 (Cu) Mach 12, gas jet T = 6K Doppler FWHM = 200 MHz Total broadening = 420 MHz Doppler vs. Mach number

Free jet laser ionization in Leuven Yu. Kudryavtsev et al., NIMB 297 (2013) 7 Measured HFS of 995(30) MHz agrees with literature: (20) MHz Doppler shift of 1830(30) MHz; gas jet velocity of 599(10) m/s Gas cell 90° bent RFQ LASER 2 LASER 1 Shaped rod segments Towards extraction RFQ Bent rf quadrupole design I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Free jet laser ionization at JYFL 63 Cu V jet ~1040 m/s FWHM = 3.9 GHz FWHM = 6.7 GHz FWHM = 1.8 GHz Laser linewidth dominated He, 180 mbar I.D. Moore et al., NIMB 317 (2013) 208 I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Borrowing ideas from rocket science ! I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Laval nozzle M. Reponen, I.D. Moore, et al., NIMA 635 (2011) cm

Fast piezo mirror Fast-switched photodiode amplifier Ti:sapphire crystal d = n λ cw Lock-in Amplifier (TEM Laselock) PSD HV out Input: CW seed laser mW Matisse TS Ti:sa (100 kHz linewidth) Output pulsed, 30 ns width 3-5 W average power 20 MHz linewidth pump laser W, 10 kHz Development of narrowband pulsed Ti:sapphire laser for gas-jet spectroscopy I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct V. Sonnenschein

 General introduction to RIB production  Practicalities of ion survival in gas  In-source laser resonance ionization  Gas jet laser ionization  Case examples and outlook Outline of talk I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Laser spectroscopy of radioisotopes (2014) N Z K Recent work mostly by collinear laser spectroscopy Mn Recent work mostly by in-source resonance ionization spectroscopy P. Campbell, I.D. Moore and M. Pearson, submitted (2014) What are limits of nuclear existence? Do new forms of nuclear matter exist? Are there new forms of collective motion? Does the ordering of quantum states change? Key questions Au Tl At

I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Challenges: moving towards heavy & rare isotopes Ac Radium is the heaviest chain of isotopes studied using optical techiques Uranium is heaviest ISOL target Heavier elements are not available Need fusion reactions in heavy-ion collisions Low production cross sections Lack of stable isotopes – lack of optical transitions

2 D 3/2 4 P 3/ nm nm g.s. continuum cm cm -1 I.P cm -1 I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Actinium (Z=89) – choice of scheme is important =438 nm transition I.P cm -1 2 D 3/2 4 P 5/ nm nm g.s. continuum cm cm -1 =418 nm transition

Recent interest in At and its IP: Targeted  therapy for cancer treatment Benchmark for theoretical chemistry of astatine Benchmark for calculations for IP( 117 Uus) Study of the rarest element on Earth (Z=85) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct CERN RILIS

229m Th ΔE ≈ 7.6 eV τ ≈ 25 mins? 3/2 [631] 5/2 [633] Nuclear clock Europhys. Lett. 61 (2003) 181 PRL 108 (2012) Gamma ray laser Tkalya, PRL 106 (2011) Nuclear Excitation by Electron Transition Izosimov, J. Nucl. Sci. Tech. Supp. 6 (2008) 1 P&T, Europhys. Lett. 61 (2003) 181 Qubit: quantum computing Direct nuclear probing with lasers I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Evolution of fundamental constants PRC 79 (2009) PRC 79 (2009)

EU Horizon proposal - nuClock I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Best optical clocks reach precision nuClock aims to utilize nuclear transition Consortium: - nuclear physics - atomic physics - quantum optics - metrology - detector- and laser development Goal 3 decades of study; over 70 publications: Direct observation of the transition? Definitive evidence of the existence of the isomer? → Collinear or gas cell/gas jet spectroscopy

Alchemy in the 21 st century I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Peak of Th, U Transfermium island Z = 114 Z = 126 Z = 124 S. Cwiok et al, Nucl. Phys. A 611 (1996) 211 Relativistic- and QED- effects gain importance for heavy elements Fm (Z=100) is heaviest element so far studied with laser spectroscopy MCDF calculations performed for No (Z=102) and Lr (Z=103) to constrain spectral regions Search for 7s7p 1 P 1 level at GSI, October 2014

Leuven (May 2012) RIKEN (Dec. 2012) In-gas Laser Ionization and Spectroscopy NETwork (IGLIS-NET) JYFL (June 2013) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct KISS (Japan) – towards identification of r process astrophysical site In-gas-cell/in-gas-jet spectroscopy at S 3, GANIL - towards N=Z line, heaviest elements PALIS, RIKEN – parasitic slow beams MARA (JYFL) – nuclei for rp-process Workshops

Thank you

Simulations: hot cavity vs. gas cell P. Campbell, I.D. Moore and M. Pearson, submitted (2014) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct Laser linewidth 1.8 GHz

First spectroscopy with the narrowband laser Tested in Mainz to measure HFS of 227 Ac ( τ 1/2 =22 y) Same transition applied by LISOL team, May 2014, on Ac AI cm -1 J=5/ cm nm J 0 =3/2 0 cm -1, 6d7s 2 IP nm Future: measure Pu via in-jet RIS followed by high resolution collinear laser spectroscopy (Mainz, Leuven, Manchester and Liverpool) In-jet RIS in the search for 229m Th (new EU Horizon 2020 application) I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Detect via the Hyperfine Structure Ion trapping of Th 3+ C.J. Campbell et al., PRL 106 (2011) C.J. Campell et al., PRL 108 (2012) Collinear or gas jet spectroscopy V. Sonnenschein, I.D. Moore et al., Eur. Phys. J A 48 (2012) 52 Towards detection of the isomer I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014

Towards the future… In-gas-cell and in-gas-jet laser ionization at S 3 facility, SPIRAL-2, GANIL Continuation of jet studies with laser ionization (nozzles etc) Spectroscopy of exotic nuclei in the jet with injection-locked lasers I.D. Moore, Advanced School on Laser Applications at Accelerators, Sept. – Oct. 2014